For example, Japanese Patent Application Laid-Open Publication No. 2008-193614 (Patent Document 1) describes a method in which VLAN-IDs are managed by dividing them into sub-group IDs and sub-IDs included therein. In this method, ports to which the same sub-group ID is allocated belong to the same flooding domain, but whether relay between the ports therein is possible is determined based on the sub-IDs.